feat: support generating shell syntax for $group INTELLIJ-197

[himanshusinghs]

Description

This PR adds support for generating shell syntax for $group stage and the supported accumulators.

Checklist

• New tests and/or benchmarks are included.
• Documentation is changed or added.
• Changelog is updated accordingly.
• I have signed the MongoDB Contributor License Agreement (https://www.mongodb.com/legal/contributor-agreement).

Open Questions

[github-actions]

Coverage Report

Overall Project	80.81% -0.22%	✅
Files changed	86.29%	✅

File	Coverage
Group.kt	94.78% -5.22%	✅
Unwind.kt	94.64%	✅
Sort.kt	92.73%	✅
Update.kt	91.79%	✅
Aggregate.kt	90.46%	✅
Find.kt	83.18%	✅
References.kt	63.51% -19.78%	🚫
Context.kt	61.88%	✅

[himanshusinghs]

@kmruiz I adopted this approach to make MongoshBackend understand when to prefix the field name with a $ and when not to. The idea is if a field reference is used in the value place then it is supposed to be true and the emitted field will be prefixed with $ otherwise not.

[github-actions]

🤖 Benchmark Comparison for feat: support generating shell syntax for $group

Benchmark	Previous	Current	Change
com.mongodb.jbplugin.jmh.SampleBenchmark.init	2,606,573,293.49 ops/s	2,627,754,671.98 ops/s	0.81%

[github-actions]

🤖 Benchmark Comparison for chore: add CHANGELOG entry

Benchmark	Previous	Current	Change
com.mongodb.jbplugin.jmh.SampleBenchmark.init	2,606,573,293.49 ops/s	2,670,051,607.07 ops/s	2.44%

[github-actions]

🤖 Benchmark Comparison for chore: rebased fixture file with that on main

Benchmark	Previous	Current	Change
com.mongodb.jbplugin.jmh.SampleBenchmark.init	2,606,573,293.49 ops/s	2,658,418,223.59 ops/s	1.99%

[github-actions]

🤖 Benchmark Comparison for chore: updated docs

Benchmark	Previous	Current	Change
com.mongodb.jbplugin.jmh.SampleBenchmark.init	2,606,573,293.49 ops/s	2,596,057,268.65 ops/s	-0.40%